Today, I am departing a bit from what I usually post. I helped a friend put up some walls, in his basement, this past weekend. We have a bit more work left, finishing the drywall, but the one thing I didn’t want to do on-site was cut down the door. If I only needed to cut off a half inch or so, I probably would have, but this door needed to lose about 4″. While there are ways to reduce tear-out when cutting down a door panel with a circular saw, I have discovered that a table saw works better. Interior doors used to be solid wood, and you could plane or cut away what-ever you needed to achieve the desired door height. Nowadays the doors are made primarily with cardboard. The Luan doors are typically made with wood, with only cardboard supporting the hollow center, but most of the colonial style doors are made with Masonite, which is basically pressed wood fibers (nearly cardboard).
I find that I get the least amount of tear-out cutting the doors down on the table saw. I just need good outfeed support, or a second person holding up the end.
The perimeter 1″ of the door is a solid piece of wood. The rest of the door is cardboard inside.
When you trim past the first inch, you need to recover or replace the wood from the bottom. There are various ways to separate the panel from the block. I have used utility knives on luan doors, and I have used chisels.
But since I was in my shop, I just cut the panel away on the table saw instead.
As long as you don’t cut into the old block, you can reuse it. Just push the cardboard back an inch or so, then scrape away any of the old glue.
Apply wood glue to the opening and/or the outside of the block, then tap it back into place.
Be sure not to tap too hard. It is really hard to get it back out flush. When the block is seated, wipe away any glue and clamp it up for at least an hour.
While the glue is drying, Mark and cut the bottom of the trim and jamb. I used my circular saw to cut away the excess on the bottom. Just pull the blade guard up and run the saw around from the top to the bottom.
If you don’t quite get it all, you can hand-saw the last little bits to remove the waste.
That is basically all you need to do.
When the glue is dry, reattach the door to the jamb.
You may wish to take the opportunity to paint or prime the bottom, especially if there are going to be any potential damp conditions. Otherwise the door is done. I saved the packaging and slid the cardboard and banding back on so everything would stay stable during transport.